A year-long investigation by US senator Chuck Grassley (R-IA) into Google's use of NASA's Silicon Valley airport has shown that the company benefited from buying cheap aviation fuel from NASA at a discounted price arranged by the Pentagon.

"Are some executives getting a special deal on fuel that isn't available to other businesses?" said the Republican Senator Glassley, who will be conducting an audit into the arrangement. He added that the Google/NASA deal raises concerns about the government being a "fair broker with businesses and responsible steward of tax dollars."

Google currently has a Boeing 767, Boeing 757, four Gulfstream V's, two helicopters, and an 1982 Dornier Alpha Jet based at Moffett Field, which is handily right next door to the Chocolate Factory's campus. The arrangement is part of a 2007 deal between NASA and Google that allows Google to rent space at the airport, with the space agency getting to use Google aircraft for experiments as the quid pro quo.

But, according toThe Wall Street Journal, Google's air force (managed by holding company H211) has also been benefiting financially by buying its aviation fuel cheap from NASA, which is supplied by the Pentagon. Documents obtained by Senator Grassley show that since 2009, H211 has bought 2.3 million gallons of jet fuel at an average price of $3.19 per gallon.

"I don't see how in the hell anybody can buy it that cheap," said Fred Fitts, president of the Corporate Aircraft Association, adding that the average price his members were paying was $4.35 per gallon.

According to FAA records, Google aircraft have flown from Moffett 710 times since 2007, which includes 20 flights to the luxurious Caribbean island of Tortola, 17 to Hawaii, and 15 to Tahiti. New York and Los Angeles are also frequent destinations, and many flights also go to Europe.

The FAA reports that three of Google's jets, including the 767, flew from Moffett last year to Croatia, where CEO Larry Page was a groomsman at his brother–in-law's wedding, and bought 24,000 gallons of fuel for the trip at a price of $3.33 per gallon, more than a dollar less than the going rate. According to H211's contract, fuel bought at Moffett should be used "for performance of a U.S. government contract, charter or other approved use."

Kenneth Ambrose, an executive with H211, said that it bought "the only fuel available at Moffett" and pays "full retail for hangar space that includes none of the ground support typically included at business aircraft hangars."

NASA does, of course, get the use of the aircraft for science, and collects $1.3m a year in rent from Page's people. According to Grassley, NASA has used Google's aircraft 115 time for atmospheric testing flights, but all but 11 of these flights have used the Chocolate Factory's Alpha Jet, rather than its much more thirsty Boeings or Gulfsteams.

"NASA is always looking for innovative, public-private partnerships to help advance our mission and provide benefit to the American taxpayer," a spokeswoman for NASA told the WSJ.

Now that the sweetheart deal with Google has been stopped, its fleet has to buy its fuel elsewhere at market prices. But the Moffett deal could soon end anyway, as Google is planning to build a $82m private terminal at Mineta San José International Airport, so that its execs can continue to fly without encountering the hoi polloi. ®